U.S. patent number 5,678,210 [Application Number 08/406,228] was granted by the patent office on 1997-10-14 for method and apparatus of coupling a transmitter to a waveguide in a remote ground terminal.
This patent grant is currently assigned to Hughes Electronics. Invention is credited to Robert Hannah.
United States Patent |
5,678,210 |
Hannah |
October 14, 1997 |
Method and apparatus of coupling a transmitter to a waveguide in a
remote ground terminal
Abstract
A remote ground terminal for transmitting a modulated data
signal to a satellite. The remote ground terminal includes an
outdoor unit comprising an input port for receiving a modulated
data signal, a housing having an upper portion and a lower portion
which comprises a waveguide. The outdoor unit further comprises a
transmitter module for amplifying and multiplying the modulated
data signal so as to produce the modulated carrier signal. The
transmitter is mounted in the lower portion of the housing so as to
be positioned above at least a portion of the waveguide. The
outdoor unit also comprises a probe having a first and second end,
with the first end being disposed in the transmitter module. The
probe receives the modulated carrier signal generated by the
transmitter module. The second end of the probe extends from a
lower surface of the transmitter module into the waveguide. The
probe is operative to couple the modulated carrier signal directly
into the waveguide disposed in the lower portion of the housing.
The modulated data signal is then coupled to an antenna coupled to
the output of the waveguide via a feedhorn, and transmitted to the
satellite.
Inventors: |
Hannah; Robert (Germantown,
MD) |
Assignee: |
Hughes Electronics (Los
Angeles, CA)
|
Family
ID: |
23607080 |
Appl.
No.: |
08/406,228 |
Filed: |
March 17, 1995 |
Current U.S.
Class: |
455/128; 333/26;
455/129; 455/81 |
Current CPC
Class: |
H04B
1/0458 (20130101) |
Current International
Class: |
H04B
1/04 (20060101); H04B 001/03 () |
Field of
Search: |
;455/81,128,129
;333/26 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Pham; Chi H.
Attorney, Agent or Firm: Whelan; John T. Denson-Low;
Wanda
Claims
What is claimed is:
1. An apparatus for transmitting a modulated carrier signal to a
satellite, said apparatus comprising:
an input port for receiving a modulated data signal;
a housing having an upper portion and a lower portion, said lower
portion of said housing comprising a waveguide;
a transmitter module for amplifying and multiplying said modulated
data signal so as to produce said modulated carrier signal, said
transmitter module being mounted in said lower portion of said
housing so as to be positioned above at least a portion of said
waveguide; and
a probe having a first and second end, said first end disposed in
said transmitter module and receives said modulated carrier signal
generated by said transmitter module, said second end extending
from a lower surface of said transmitter module into said
waveguide;
wherein said probe is operative to couple said modulated carrier
signal directly into said waveguide disposed in said lower portion
of said housing.
2. The apparatus of claim 1, wherein said waveguide disposed in
said lower portion of said housing comprises a substantially
rectangular shape, and extends substantially parallel to the lower
surface of the transmitter module.
3. The apparatus of claim 2, wherein said lower portion of said
housing comprises a dielectric rod having a hollow center which is
disposed in said waveguide and extends upwardly through said lower
portion of said housing so as to engage said lower surface of said
transmitter module, said probe positioned in the hollow center of
said dielectric rod operative.
4. The apparatus of claim 3, wherein said dielectric rod comprises
Teflon.
5. The apparatus of claim 1, wherein said probe is orthogonal to
said lower surface of said transmitter module and to the
longitudinal plane of said waveguide disposed in said lower portion
of said housing.
6. The apparatus of claim 1, wherein said lower portion of said
housing is formed such that said waveguide is an integral part of
said lower portion of said housing.
7. The apparatus of claim 6, wherein said waveguide formed as an
integral part of said housing is a WR-75 Ku band waveguide.
8. The apparatus of claim 1, wherein said upper and lower portions
of said housing comprise a plurality of heat sinks disposed on an
outer surface of said upper and lower portions of said housing.
9. The apparatus of claim 8, wherein said lower surface of said
transmitter module is mounted flush with a surface of said lower
portion of said housing which is integral with said plurality of
said heat sinks.
10. A method for coupling a modulated carrier signal generated by a
transmitter module to an antenna comprising:
forming an outdoor unit having an upper portion and a lower
portion, said lower portion of said outdoor unit comprising a
waveguide;
mounting said transmitter module in said lower portion of said
outdoor unit so as to be positioned above at least a portion of
said waveguide; and
connecting a probe having a first and second end between said
transmitter module and said waveguide, said first end of said probe
being disposed in said transmitter module and coupled to an output
of said transmitter module so as to receive said modulated carrier
signal, said second end of said probe extending from a lower
surface of said transmitter module into said waveguide;
wherein said probe is operative to couple said modulated carrier
signal directly into said waveguide disposed in said lower portion
of said outdoor unit.
11. The method of claim 10, wherein said waveguide disposed in said
lower portion of said outdoor unit comprises a substantially
rectangular shape, and extends substantially parallel to the lower
surface of the transmitter module.
12. The method of claim 11, further comprising disposing a
dielectric rod having a hollow center in said waveguide, said
dielectric rod extending upwardly through said lower portion of
said housing so as to engage said lower surface of said transmitter
module, said dielectric rod operative to locate said probe in the
proper position during assembly.
13. The method of claim 12, wherein said dielectric rod comprises
Teflon.
14. The method of claim 10, wherein said probe is orthogonal to
said lower surface of said transmitter module and to the
longitudinal plane of said waveguide disposed in said lower portion
of said outdoor unit.
15. The method of claim 10, wherein said lower portion of said
outdoor unit is formed such that said waveguide is an integral part
of said lower portion of said outdoor unit.
16. The method of claim 15, wherein said waveguide formed as an
integral part of said outdoor unit is a WR-75 Ku band
waveguide.
17. The method of claim 10, further comprising forming a plurality
of heat sinks on an outer surface of said upper and lower portions
of said outdoor unit.
18. The method of claim 17, wherein said lower surface of said
transmitter module is mounted flush with a surface of said lower
portion of said housing which is integral with said plurality of
said heat sinks.
Description
BACKGROUND OF THE INVENTION
Satellite communication systems typically have employed large
aperture antennas and high power transmitters for establishing an
uplink to the satellite. Recently, however, very small aperture
antenna ground terminals, referred to as remote ground terminals,
have been developed for data transmission at low rates. In such
systems, the remote ground terminals are utilized for communicating
via a satellite from a remote location to a central hub station.
The central hub station communicates with multiple remote ground
terminals, and has a significantly larger antenna, as well as a
significantly larger power output capability than any of the remote
ground terminals.
Very small aperture terminal (VSAT) remote terminals can be used to
communicate data, voice and video, to or from a remote site to a
central hub. Typically, the VSAT remote terminals have a small
aperture directional antenna for receiving from or transmitting
signals to a satellite, and an outdoor unit (ODU) mounted near the
antenna for transmitting a modulated carrier generated by an indoor
unit (IDU). The IDU demodulates incoming signals received from the
ODU and also operates as an interface between a user's
communication equipment and the ODU.
The outdoor unit functions in part as an interface between the
indoor unit and the antenna. As such, it contains a transmitter
chain for transmitting the modulated carrier signal in accordance
with data signals received from the indoor unit and a receiver
chain for coupling signals received via the antenna to the indoor
unit. Both the transmitter and receiver chains comprise discrete
modules which are interconnected, as required, by various cables
and connectors.
For example, prior art outdoor units utilized a cable to couple the
output of a transmitter module to a waveguide, which is also
coupled to the antenna. However, such an interface necessitates the
output signal traverse two additional connectors, one at the output
of the transmitter module and one at the input to the waveguide.
Accordingly, the signal output by the transmitter module is
attenuated prior to entering the waveguide due to the power losses
associated with the standing wave ratio loss created by the
additional connectors and cable. As a result, the transmitter
module must provide an output signal having increased output power
levels so as to compensate for these additional losses.
Furthermore, this technique requires the use of additional
connectors and cables. Both the foregoing requirements operate to
increase the cost of the outdoor unit.
As the viability of the remote ground terminal concept increases as
the cost for providing a remote ground terminal at the remote
location decreases, it is necessary to decrease the cost of all
components of the remote ground terminal as much as possible.
Accordingly, in order to minimize the power level of the signal
produced by the transmitter module, there exists a need for an
outdoor unit which minimizes the transmission losses incurred in
coupling the output of the transmitter module to the antenna, and
which minimizes the number of components required to couple the
transmitter module to the antenna.
SUMMARY OF THE INVENTION
The present invention provides an outdoor unit of a remote ground
terminal designed to satisfy the aforementioned needs.
Specifically, the present invention provides a novel design for
coupling the output of the transmitter module to a waveguide that
is simple, eliminates the need for additional connectors or cables,
and minimizes the transmission loss associated with transferring a
signal output by the transmitter module to the waveguide so as to
substantially reduce the overall cost of the remote ground terminal
relative to prior art designs.
Accordingly, the present invention relates to an apparatus for
transmitting a modulated carrier signal to a satellite. In one
embodiment, the apparatus comprises an input port for receiving a
modulated data signal, a housing having an upper portion and a
lower portion which comprises a waveguide. The apparatus further
comprises a transmitter module for amplifying and multiplying the
modulated data signal so as to produce the modulated carrier
signal. The transmitter module is mounted in the lower portion of
the housing so as to be positioned above at least a portion of the
waveguide. The apparatus of the present invention also comprises a
probe having a first and second end, with the first end being
disposed in the transmitter module. The probe receives the
modulated carrier signal generated by the transmitter module. The
second end of the probe extends from a lower surface of the
transmitter module into the waveguide. The probe is operative to
couple the modulated carrier signal directly into the waveguide
disposed in the lower portion of the housing. The modulated data
signal is then coupled to an antenna via a feedhorn coupled to the
output of the waveguide, and transmitted to the satellite.
As described below, the apparatus of the present invention provides
important advantages. For example, the present invention eliminates
the need for an additional cable to connect the transmitter module
with the waveguide coupled to the transmitting antenna. This
minimizes the power losses associated with coupling the output of
the transmitter module to the waveguide. As a result, the power
rating of the amplifier of the transmitter module can be reduced
thereby reducing the cost of the module. The present invention also
eliminates the cost associated with the additional cable and the
connectors, thereby further reducing the cost of the outdoor
unit.
Another advantage is that the transmitter module mounts flush with
a surface which is integral with heat dissipating elements of the
outdoor unit, thereby increasing the efficiency of the heat
dissipation of the outdoor unit.
The invention itself, together with further objects and attendant
advantages, will best be understood by reference to the following
detailed description, taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a very small aperture terminal
("VSAT") satellite communication network which utilizes the present
invention.
FIG. 2 is a block diagram illustrating one embodiment of the
outdoor unit of the present invention.
FIG. 3 is a block diagram illustrating the components of one
embodiment of the transmitter module of the present invention.
FIG. 4 is a drawing illustrating the physical dimensions of one
embodiment of the transmitter module of the present invention.
FIG. 5 is a drawing illustrating the lower housing of the outdoor
unit of the present invention.
FIG. 6 is a cross sectional drawing of the lower housing of the
outdoor unit of the present invention illustrating the
interconnection between the lower housing and the transmitter
module.
FIG. 7 illustrates an exploded view of the transmitter module
positioned to be installed in the lower housing of the outdoor unit
of the present invention.
FIG. 8 illustrates an exploded view of the transmitter installed in
the lower housing of the outdoor unit of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
The VSAT satellite communication network 10 illustrated in FIG. 1,
comprises a central hub station 2, a communication satellite 4, and
a plurality of remote ground terminals 6 (only one is shown). The
VSAT network 10 functions as a two way transmission system for
transferring data and voice communications between the central hub
station 2 and the numerous remote ground terminals 6. All data is
transferred between the central hub station 2 and the remote ground
terminals 6 via transponders located in the satellite 4. Signals
transmitted from the central hub station 2 to the remote ground
terminal 6 are referred to as "outroute", while signals transmitted
in the opposite direction are referred to as "inroute".
The remote ground terminal 6 comprises a small aperture antenna 12
for receiving (i.e., downlink) and transmitting (i.e., uplink)
signals, an outdoor unit 14 typically mounted proximate the antenna
12 which comprises a transmitter module for amplifying and
frequency multiplying a modulated data signal which is coupled to
the antenna 12 via a feedhorn 27, and an indoor unit 16 which
operates as an interface between a specific user's communication
equipment and the outdoor unit 14. The indoor unit 16 also
generates the modulated data signal which is amplified and
frequency multiplied by the transmitter module of the outdoor
unit.
The present invention provides an outdoor unit 14 which eliminates
the need for connectors and cables to couple the output of a
transmitter module 20 to a waveguide 21 which is coupled to the
antenna 12. As a result, the present invention minimizes the
transmission losses incurred in coupling the output of the
transmitter module 20 to the waveguide 21. The reduction of
transmission losses allows for a reduction in the output power
requirements of the transmitter module 20, which results in a
substantial reduction in the cost of the transmitter module 20.
FIG. 2 is a block diagram of the outdoor unit 14 of the present
invention. A shown in FIG. 2, the outdoor unit 14 of the present
invention comprises a multiplexer 22 for receiving the modulated
data signal from the indoor unit 16, a main transmit module 24,
which includes a phase-locked loop 29 and a frequency multiplier 32
for frequency stabilizing and multiplying the modulated data
signal, a transmitter module 20 for amplifying and frequency
multiplying the modulated data signal to generate a modulated
carrier signal, and an orthogonal waveguide transition ("OWT") 25
which couples the output of the transmitter module 20 to a transmit
receive isolation assembly ("TRIA") 26. The output of the TRIA
assembly 26 is coupled to the antenna 12 via a feedhorn 27. The
antenna 12 then transmits the modulated carrier signal to the
satellite 4.
The outdoor unit 14 also comprises a receiver chain for receiving
the downlink signal from the satellite 4. The receiver chain
comprises a low noise block downconverter 28 which transforms the
received signal into a corresponding intermediate frequency signal.
This signal is then coupled to the indoor unit 16, where it is
further demodulated so as recreate the transmitted data.
As stated, the input of the transmitter module 20 is coupled to the
output of the frequency multiplier 32 of the main transmit module
24. The transmitter module 20 functions to amplify and frequency
multiply the signal output by the frequency multiplier 32 so as to
produce a modulated carrier frequency suitable for transmission to
the satellite 4. As shown in FIG. 3, in one embodiment, the
transmitter module 20 comprises an input buffer 33, a frequency
multiplier 34 which multiplies the second intermediate frequency by
a factor of 4, a bandpass filter 35 tuned to the frequency of the
carrier signal and an amplifier 36 for amplifying the output of the
frequency multiplier 34 of the transmitter module 20, which are all
coupled in a series configuration.
Turning to FIG. 4, the output of the transmitter module 20 is
coupled to an rf feed-through 37, referred to as a probe. As shown
in FIG. 4, this probe 37 extends downwardly from the transmitter
module 20, orthogonally to the bottom surface 38 of the module 20.
The first end of the probe 37 (not shown), which is internal to the
transmitter module 20, is coupled to the output of the amplifier
36. In one embodiment, this coupling comprises a shielded wire
suitable for transferring the carrier signal having one end
connected to the amplifier 36 output and the other end connected to
the probe 37. The second end 39 of the probe 37 extends into a
waveguide 21 disposed in a lower housing 41 of the outdoor unit 14,
as shown in FIGS. 6-8.
Referring to FIG. 4, the transmitter module 20 also comprises input
pins 66 for receiving DC power, a control line input pin 65 and an
rf connector 67 for receiving the output of the main transmit
module 24 extending from the bottom surface 38 of the transmitter
module 20.
The housing of the outdoor unit 14 comprises an upper and lower
housing, which are mated together to form the shell of the outdoor
unit 14. FIG. 5 illustrates the lower housing 41 of the outdoor
unit 14, viewed from opposite ends. Typically, both the upper and
lower housing are made of metal and comprise a plurality of heat
sinks 42 disposed on the outer surfaces thereof to dissipate the
heat generated by the transmitter module 20 and the other
components contained in the outdoor unit 14. The waveguide 21 is
formed as an integral part of the lower housing 41.
FIG. 6 is a cross-sectional view of a portion of the lower housing
41 of the outdoor unit 14 with the transmitter module 20 installed
therein. As shown in FIG. 6, the lower housing 41 comprises the
waveguide 21 having a rectangular shape which extends parallel to
the bottom surface 38 of the transmitter module 20. The waveguide
21 has a longitudinal plane which is also parallel to the bottom
surface 38 of the transmitter module 20. The waveguide 21 extends
to a side of the lower housing 41. The TRIA assembly 26 (not
shown), which is also a waveguide assembly, is mounted to the side
of the lower housing 41 at the opening of the waveguide 21. In the
first embodiment, the waveguide 21 formed is a WR-75 Ku band
waveguide.
The lower housing 41 further comprises a dielectric rod 43 having a
hollow center which is disposed in the waveguide 21. The dielectric
rod 43, which can be formed from TEFLON, functions to locate the
probe 37 extending from the transmitter module 20 in the proper
location. The dielectric rod 43 is orthogonal to the longitudinal
plane of the waveguide, and extends from the bottom surface 44 of
the waveguide 21 through the portion of the lower housing forming
the upper surface 68 of the waveguide 21 so as engage the bottom
surface 38 of the transmitter module 20.
During assembly, the probe 37 is inserted into the dielectric rod
43 until the bottom surface 38 of the transmitter module 20 is
flush with an upper surface 45 of the lower housing 41 forming the
waveguide 21. The transmitter module 20 is then secured to the
lower housing 41. As seen from FIG. 6, the transmitter module 20
extends over a portion of the waveguide 21. Once assembled, both
the probe 37 and the dielectric rod 43 are orthogonal to the bottom
surface 38 of the transmitter module 20 and the longitudinal plane
of the waveguide 21.
During operation, the probe 37 functions to transfer the modulated
carrier signal output by the amplifier 36 of the transmitter module
20 to the waveguide 21. The modulated carrier signal is then
coupled to the TRIA assembly 26 via the waveguide 21, and
subsequently to the antenna 12 which is coupled to the output of
the TRIA assembly 26 via a feedhorn 27.
FIGS. 7 and 8 provide an exploded view of the interconnection
between the transmitter module 20 and the lower housing 41 of the
outdoor unit 14. Specifically, FIG. 7 illustrates the transmitter
module 20 positioned to be installed in the lower housing 41, while
FIG. 8 illustrates the transmitter module 20 installed. As shown in
FIGS. 7 and 8, during installation, the probe 37 which extends
downwardly from the transmitter module 20 is positioned directly
above the dielectric rod 43 disposed in the waveguide 21. The
transmitter module 20 is then lowered such that the probe 37 enters
the center of the dielectric rod 43. The transmitter module 20 is
then lowered further until the bottom surface 38 of the transmitter
module 20 is flush with the upper surface 45 of the lower housing
41.
The dimensions of the probe 37 and the waveguide 21 vary in
accordance with the frequency of the modulated carrier signal to be
transmitted. The dimensions of the components illustrated in FIGS.
7 and 8 allow for the transfer of a modulated carrier signal in the
Ku frequency band (i.e., 14.0 Ghz to 14.5 Ghz).
Referring to FIGS. 4, 7 and 8, the probe 37 has a diameter of 0.050
inches, and a length of 0.375 inches. The upper wall 70 of the
waveguide 21 has a height of 0.250 inches. The height of the
waveguide opening is 0.375 inches. The dielectric rod 43 has a
height of 0.625 inches and is positioned along the longitudinal
axis of the waveguide 21 such that the probe 37 is 0.175 inches
from the rear wall 47 of the waveguide 21. The length of the
waveguide 21 is variable in accordance with manufacturing
requirements.
Accordingly, for transmission in the 14.0-14.5 Ghz frequency band,
the two critical dimensions are that the probe 37 extends 0.125
inches into the waveguide 21, and that the probe 37 is positioned
0.175 inches from the rear wall 47 of the waveguide 21. The output
of the waveguide 21 is coupled to the TRIA assembly 26 which
functions to couple the modulated carrier signal to the antenna 12
via a feedhorn 27. The modulated carrier signal is then transmitted
to the satellite 4.
The orthogonal waveguide transition of the present invention
provides numerous advantages. For example, the present invention
eliminates the need for an additional cable to connect the
transmitter module with the waveguide coupled to the TRIA assembly.
This minimizes the power losses associated with coupling the output
of the transmitter module to the waveguide. As a result, the power
rating of the amplifier of the transmitter module can be reduced
thereby reducing the cost of the transmitter module. The present
invention also eliminates the cost associated with the additional
cable and the connectors, thereby further reducing the overall cost
of the outdoor unit.
Another advantage is that the transmitter module mounts directly
(i.e., flush) with a surface which is integral with the heat
dissipating surface of the outdoor unit, thereby increasing the
efficiency of the heat dissipation of the outdoor unit.
Numerous variations of the foregoing invention are also possible.
For example, while the dimensions and operational frequencies
described above relate to a unit designed to operate in the Ku
frequency band, the foregoing invention can be utilized in units
operating in various frequency bands, such as the C band.
Of course, it should be understood that a wide range of other
changes and modifications can be made to the preferred embodiment
described above. It is therefore intended that the foregoing
detailed description be regarded as illustrative rather than
limiting and that it be understood that it is the following claims,
including all equivalents, which are intended to define the scope
of the invention.
* * * * *